1. Field of the Invention
The present invention relates to polymeric materials, particularly biocompatible polymeric materials which can be used in biological applications such as wound dressings, artificial skin, tissue encasement or replacement and vascular replacement or repair.
2. Background of the Art
One of the more significant limitations in the practice of medical procedures which implant replacement materials or protect exiting materials within the body is a limitation on the supply and amount of materials which can be used within living tissue without damage to the patient or tissue, or stimulation of immune responses within the body. There are basically three classes of materials which are considered biocompatible and used in medical procedures. Inert inorganic materials (such as Nitonol.TM. metal, titanium, inorganic oxides [especially as ceramics]), organic synthetic polymers which attempt to replicate naturally occurring organic materials (e.g., polyamides), composites; and harvested natural tissues and materials (e.g., veins, arteries, placental tissue, corneas, etc.). Although some of these materials have generally been regarded as biocompatible, they may still stimulate immune responses, may not satisfactorily replace specific biological materials for which substitution is needed, or (in the case of harvested materials) may cause collateral damage to the patient (as in by-pass surgery with self-donated vasculature).
Although more than three hundred thousand by-pass surgeries are performed each year, there are approximately another three hundred thousand patients for whom the surgery would be beneficial, but for whom the surgery is not available. At least one reason why this surgery can not readily be performed on these potential patients, many of whom are women, is the fact that their vasculature tends to be relatively smaller, which small size does not lend the patient's system to this type of surgery. Especially where relatively small vasculature from one part of the body (e.g., the normal selection of material from the inseem of the thigh) must be used to replace veins and arteries around the heart (which tend to be relatively large), the limitations in size available can dictate against the surgery.
U.S. Pat. No. 4,411,893 describes topical therapeutic compositions which comprise 0.1 to 70 percent by weight of a water-soluble tertiary amine oxide and a therapeutic agent selected from erythromycin, benzoyl peroxide, hydrocortisone, tetracycline, 5-fluorouracil and propranolol. The amine oxide is described as enhancing the penetration of the therapeutic agent through the skin. Hydrophilic polymer additives such as acrylic polymers, polyvinyl alcohol, gelatin, hydroxyethyl cellulose, carboxymethyl cellulose, natural gums and other thickening agents are also described.
U.S. Pat. No. 3,508,941 describes a method of preparing polymers from a mixture of cyclic amine oxides and other polymers. Two different polymers, which may be selected from a wide range of natural and synthetic polymers, are dissolved together in a common solvent and then precipitated from the cosolution. It is asserted that there may be chemical reactions between the constituent polymers, which reactions create physical properties different from those of the either of the individual polymer components. In addition, the polymers may be physically joined by strong interpolymer hydrogen bonding. The polymers, for example, may be selected from amongst those a) having the capacity for strong intermolecular bonding and those b) which have the same or similar capacity or polymers having less than but at least some capacity for intermolecular hydrogen bonding. Polymers generally described include, for example, those containing atoms from Groups V-A or VI-A of the periodic table, preferably with nitrogen atoms in amine or amide groups, and/or oxygen atoms such as in carbonyl groups, hydroxyl groups, ether groups and the like. Typical polymers within this generic disclosure include, for example, poly(vinyl acetates), poly(vinyl alcohols), poly(esters), poly(saccharides, cellulose, starch, poly(anhydroglucose), poly(diethylaminoethylanhydroglucose), gum arabic, poly(amides), poly(vinylpyrrolidones), polymeric proteins or polypeptides (such as wool, silk, gelatin, hair, and the like), etc. The amine oxide is preferably cyclic mono(N-methylamine-N-oxide.
U.S. Pat. No. 2,179,181 (Graenacher et al.) describes the use of oxides of ternary amines, including heterocyclic amines, to dissolve cellulose.
Manufacturing information on Tencel.TM. fibers which is provided by Courtalds Corporate Technology, Coventry, England indicates that this fiber material is produced by direct solvent spinning procedures from amine oxides, such as NMMO, N-methylmorpholine-N-oxide. The process is taught to provide a highly oriented cellulose fiber in an environmentally benign manner. The amine oxide solvent is readily recoverable from the process, as the dissolved polymer is extruded into water, with the NMMO being readily recoverable from the water and having extremely low volatility.